The automotive industry impacts the lives and livelihood of people in the industrialized countries of the world more than any other single industry. The costs of manufacturing and operating automobiles, for example, comprise a significant portion of the cost of living to the average citizen of these countries. Lowering these costs while maintaining or improving quality is a continuing aim of the industry, its customers and their governments.
There are, of course, myriad components and subassemblies of the average automobile, for example, each of which is the target of engineers seeking cost savings. One of these is the sheet metal panels which make up the body of the automobile, or components of the body. A method which has recently been found effective in reducing both the costs of manufacturing and operation is the manufacture of body panels using what have come to be known as "tailored" blanks. For example, in the manufacture of inner door panels for automobile doors, a customized or "tailored" blank is formed by welding together two or more pieces of sheet steel which vary in thickness and/or other physical properties.
By nesting many small sheet components together during the blanking or cut-off process, the amount of scrap produced can be drastically reduced. In one known instance, a complex component with five separate pieces laser welded together reduced the scrap produced by 75% over conventional manufacturing techniques wherein the blank is formed in one piece.
In addition, by forming a customized or "tailored" blank from pieces of different thicknesses, different hardness and/or different coatings by laser welding them together along joint edges the final part, after forming in a press, for example, can exhibit certain desired characteristics in one or more areas of the part and other desired characteristics in other areas. To illustrate, it may be desirable to form an inner door panel that has a very deep draw depth to accommodate the contour of the finished vehicle door. This requires a very soft and relatively thin metal. However, the front edge of the same door, where hinges will attach the door to the vehicle, must be strong enough to support the weight of the entire door. Traditionally, this would have required the addition of several parts to a one piece stamping in order to strengthen the front edge. These parts would, of course, require separate blanking, stamping, welding and then attachment to the previously formed, one piece inner door panel.
By producing a tailored blank with a large, thin, soft piece of flat material joined to a thicker, stronger piece of flat material, a customized blank can be formed into a one piece inner door, deeply drawn in one area and very strong in another. This eliminates the necessity of fabricating additional components and attaching them. In addition, substantial savings are realized in scrap reduction and weight reduction, as well as achieving superior dimensional accuracy in the final part. The reduced weight translates into greater fuel efficiency. The increased accuracy translates into improved quality and greater customer satisfaction.
Tailored blanks were first produced in the U.S. as early as 1967, by the A.O. Smith Company. Welding in this early application was accomplished using electron beam technology.
The first significant installation relating specifically to automotive body panels was put into production by Thyseen Stahl AG in Germany in 1985. That installation, which used laser welding technology available at the time, continues in use today.
In North America, laser welding of tailored blanks began and grew slowly in the 1986-1988 period. Armco Steel, Thyssen Stahl AG and DCT-Utilase all had projects underway. Internationally, other than in Germany, Toyota in Japan and Renault in France began limited laser welding operations producing tailored blanks.
From 1989 onward, as significant improvements in laser power and blank edge preparation were made, and as processing experience accumulated, laser welding of tailored blanks became more popular. Littell International, Inc. (VIL) assignee of the present invention and application, was in the forefront although TWB-Thyssen/Worthington and DCT-Utilase were also active. The completion by VIL of a laser welding system for tailored blanks at a General Motors-Canada plant in 1994 was the last major step forward in this technology, i.e., prior to the inventions disclosed in the present application.
It should be pointed out here that many of the more traditional methods of thin material welding, e.g., resistance welding, induction welding and electron beam welding, have also been evaluated or employed in the development of manufacturing techniques for tailored blanks. While each of these techniques has certain advantages related to finished part formability, finished part appearance, processing speed or cost factors, none to date has produced the quality desired at the speed and cost desired.